function M = Lx(U)
% LX - x方向的TVD格式,的左特征矩阵
%  
    [rho,u,v,p]=U2Variables(U);
    gamma = 1.4;
    e = U(4);
    a = sqrt(gamma*p/rho);
    s1 = u^2+v^2;
    s2 =(gamma-1)/(a^2);
    s3 = s1*s2;
    M = [u/(2*a)+s3/4, -1/(2*a)-u*s2/2,-v*s2/2,s2/2;
         -v,           0,              1,      0;
         1-s3/2, u*s2, v*s2, -s2;
         -u/(2*a)+s3/4, 1/(2*a)-u*s2/2, -v*s2/2, s2/2];
end